PAR::Filter::Crypto is Filter::Crypto::CryptFile for PAR. Albeit, I can't figure out if there is a way to make it to ask for the encryption key whenever I run the program. As it is, it does not even ask for key when it encrypts and creates the PAR - it uses a key created at install-time.

Reading at the other links you provided, maybe PAR::Filter::Crypto is not the way to go after all.